Transverse tapper assembly for sifter sieve stack

ABSTRACT

A tapper assembly for the sieve stack of a reciprocating air column sifter includes a mounting ring that is incorporated into the stack. The ring mounts two oppositely disposed transverse tappers which are alternately electromagnetically actuated to tap the sieve above the mounting ring.

United States Patent Schurrer 1 Oct. 24, 1972 54] TRANSVERSE TAPPER ASSEMBLY [56] References Cited FOR SIFTER SIEVE STACK UNHED STATES PATENTS m] Invent: w Mlwaukee 3,521,750 7/1970 Hamilton ..209/3s2 x 6,366 4/1849 Johnston ..209/3s2 [73] Assignee: ATM Corporation, Greendale, Wis. 789,259 5/1905 Cornwall ..209/382 X 3,366,237 l/l968 Shum ..209/382 x 22 Filed: Oct. 15, 1970 21 A l N J 1 094 Primary Examiner-Frank W. Lutter 1 PP 0 Assistant ExaminerWilliam Cuchlinski, Jr.

. Attorney-Allan W. Leiser and Arthur H. Seidel [52 us. c1. ..209/237, 209/315, 209/347,

' 209/382, 210/388 [57] ABSTRACT [51] Int. 6!. ..B07b 1/54 A tapper assembly for the sieve stack of a reciprocat- [58] Field o1 Search ..209/382, 381, 237, 334, 347, ing air column Sifter includes a mounting ring that is incorporated into the stack. The ring mounts two 0ppositely disposed transverse tappers which are alternately electromagnetically actuated to tap the sieve above the mounting ring.

4 C a m 4 Drawing Figures PATENTEUUBT 24 I972 SHEET 1 UP 2 INVENTOFi ATTORNEY PATENTEU um 24 I972 SHEET 2 BF 2 INVENTOR wmwfi ATTORNEY TRANSVERSE TAPPER ASSEMBLY FOR SIFIER SIEVE STACK BACKGROUND OF THE INVENTION This invention relates to a tapper for the sieve stack of a sifter. The tapper of the invention is particularly suited, but not limited, to use in a reciprocating air column sifter such as that shown in U.S. Pat. No. 3,366,234, issued Jan. 30, 1968.

All sifters need occasional mechanical tapping to clear the sifting screen or screens. Reciprocating air column sifters, in which a reciprocating column of air is used to enhance the sifting action, require an absolute minimum of mechanical tapping, but even in such sifters tapping is sometimes necessary to prevent the buildup of small deposits on extremely fine screens, for example screens in thefive to thirty-seven micron region, which deposits could interfere with air flow. U.S. Pat. No. 3,366,237, issued Jan. 30, 1968, shows a vertical or axial tapper for a reciprocating air column sifter which acts axially against the end of the entire sieve stack, but

it has also been found desirable to provide a transverse I tapper which can act on a particular sieve in a column.

SUMMARY OF THE INVENTION This invention contemplates a. transversely acting tapper that is actuallyincorporated in a sieve stack assembly and that carries one or more tappers which act upon the rigid outer ring of the next adjacent sieve. The tapper of the invention is highly effective, durable, and relatively simple and inexpensive to manufacture, assemble, and use. Other objects and advantages of the invention will appear from the description to follow.

BRIEF DESCRIPTION OF THEDRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT The portion of the sieve stack assembly shown by FIG. 1 includes, from top to bottom, a pair of sieves l, the tapper assembly of the invention which is designated generally by the reference numeral 2, and a spacer ring 3, all in vertically stacked relation. These elements will,'of course, be incorporated in or serve as the sieve stack assembly of a sifter, the sifter as a whole not being shown because of the construction of such sifters is known to those skilled in the art, and because the tapper of this invention is suitable for use in any of a number of different types of sifters. The particular components shown have been designed for incorporation into a sifter like that shown in the aforesaid U.S.

Pat. No. 3,366,234, to which reference may be had for a further description, in which event a speaker or sonic vibrator would be above and facing the sieves 1. It should also be appreciated that there may be more sieves placed above the sieves 1 and one or more additional sieves might be placed below the tapper 2. In the usual case, however, the tapper 2 will be placed below the lowest or fines sieve if more than one sieve is used. The terms sieve stack and sieve stack assembly as used in this description and the appended claims are intended to cover any arrangement in which there is at least one sieve adapted to be stacked with the tapper assembly of the invention.

The sieves l are preferably of the type shown in U.S. Pat. No. 3,386,580, issued June 4, 1968, to which reference may be had for a further description, and they are substantially identical except that the lowermost has a finer screen. Each sieve 1 includes a horizontally split, rigid, transparent outer ring 4 with a screen 5 clamped between the parts thereof. The upper inner edge 6 of the ring 4 is stepped, as is the outer lower edge 7, and as a result a number of sieves 1 can be stacked to form a smooth, continuous column.

The spacer 3 is a ring of the same general configuration as the sieve ring 4, but is unitary and carries no screen. Such a spacer is usually interposed between the tapper 2 and a fines collection bag or outlet (not shown), although this is not absolutely necessary.

The tapper 2 includes a mounting ring 8, preferably formed of aluminum or some other non-magnetic metal, which has the same configuration as the sieve rings 4 although the outer diameter is slightly smaller, and is stacked with and immediately adjacent to the lower sieve l to define a continuous air column.

Mounted on opposite outside surfaces of the ring 8 are two tappers 9. The tappers 9 are substantially identical, except that one has a slightly larger housing to admit an electrical connector as will be described, and so only the right hand tapper 9 as seen in FIG. 1 is shown and described in detail herein.

As can be seen in FIGS. 2 and 3, an outwardly facing, U-shaped bracket 10 is mounted on the ring 8 by means of screws 11. A substantially closed, box-like metal housing 12 is mounted on the legs of the bracket 10 by means of opposite screws 13 and serves to enclose the operating elements of the tapper 9. The housing 12 for the right hand mechanism 9 as seen in FIG. 1 extends upwardly further than the housing for the other tapper, simply to provide space for the entry of an electrical conductor 14 to provide power to the operating elements. The main portion of the housing 12 is box-like and defines the top and four walls of the enclosure, and the bottom wall is formed by a separate piece 12 which is bent upwardly at opposite sides to define ears 12" which are also secured by the screws 13.

An L-shaped stationary magnetic arm 15, which is attached to the bracket 10 by the screws 11, includes a vertical leg which faces and extends above the mounting ring 8, and a horizontal leg 16 which extends outwardly into the housing 12. The vertical leg of the arm 15 is in the plane of the front wall of the housing 12, the wall toward the ring 8, and the housing wall is suitably cut out to accomodate the same. The arm 15 is formed of any suitable magnetic material, and a non-magnetic spacer 17 is inserted between it and the base portion of the bracket 10. A tubular magnetic 'core 18 is suitably fixed to the vertical leg of the arm 15 and extends transversely therethrough to face the sieve ring 4 at the level of the screen 5 which is approximately its vertical midpoint. The core 18 is provided with a central, horizontal bore 19 which has an enlarged portion 20 at its inner end.

An electrical operating coil 21 is wound on an insulating spool 22 which is fitted on the outside of the core 18 and held in place by means of a retainer ring 23. There is a suitable electrical connection (not shown) between the coil 21 of the right hand tapper 9 as seen in FIG. 1 and the conductor 14, and a second set of connections (also not shown) leads around the ring 8 to the coil 21 of the opposite mechanism 9. The ring 8 is provided with an annular groove 24 to accommodate connecting wires, and after the wires are in place they are preferably covered by aluminum tape 25.

A cylindrical tapper pin 27, preferably formed of nylon, is reciprocally slidably received in the bore 19 to be aligned with the lower sieve 1, and has an enlarged head 28 at its inner end which is adapted to strike against the ring 4 of the sieve l. A compression spring 29 seated in the enlarged bore portion 20 bears against the head 28to urge the pin 27 to the left as seen in FIG.

3 so that it is always against the ring 4 to insure maximum transmission'of energy from the tapper bar 31. A

retainer ring 30 limits movement of the pin 27 to the left. When the head 28 is against the ring 4, the outer or right hand end of the pin 27 projects slightly beyond the core 18.

A moveable, L-shaped tapper bar 31, also formed of a suitable magnetic material, has a lower horizontal leg 32 which faces and substantially overlaps the stationary bar leg 16, and a generally vertical leg 33 which faces and is adapted to engage the projecting outer end of the pin 27. A resilient leaf spring 34 lies between and has its ends riveted to the legs 16 and leg 32 and normally holds the leg 33 in the retracted position'shown in FIG. 3 where it is spaced from the outer end of the pin 27.

Upon energization of he coil 21, the leg 33 will be magnetically attracted toward the core 18 in a counterclockwise movement against the force of the spring 34, and in the course of this movement it will move to an operating position where it delivers a light blow to the outer end of the pin 27. This force is transmitted therethrough to the rigid sieve ring 4 to provide a tapping action which will clear the screen 5 of any residual particles. Upon de-energization of the coil 21, the spring 34 will return the leg 33 to the clockwise or retracted position shown in FIG. 3. The substantial overlap between the legs 32 and 16 insures a strong magnetic circuit to insure an adequate tapping action.

Although a single tapper 9 might be suitable, the preferred embodiment shown includes the two tappers 9 on opposite sides of the ring 4, and these are preferably operated alternately to deliver alternating taps to opposite sides of the ring 4for enhanced action. In the usual situation for a screen of 5-37 micron size, it is desirableto have one of the tappers actuated every two seconds, delivering a total of 30 taps per minute, fifteen to each side.

Fig. 4 shows one suitable electrical circuit for actuating the tappers although any of a number of possible circuits might be used. In the circuit of FIG. 4, the two tapper coils 21 are connected in parallel across a power supply 35. In, the preferred embodiment, the power supply 35 is the same a c source used to operate the reciprocating air column sifter, and a diode rectifier 36 and limiting resistance 37 are included in the coil circuit to provide a suitable d-c current. If desired, a separate d-c source could of course be used. Also, a main on-off switch 38 is inserted in the circuit for activating and deactivating the tappers 9.

Each coil 21 is connected in series with a respective set of normally open contacts 39, and these are controlled by a conventional cam-type timer motor 40 which is also connected across the source 35. As the motor 40 operates, the cam will revolve and alternately briefly close the contact 39 for one or the other coil 21. The energizing power for the coils 21 is supplied by a large capacitor 41, about microfarads in the preferred embodiment, connected in parallel with the coils 21. The capacitor 41 is charged when the main switch 38 is closed, and-will discharge through one or the other coil 21 when the respective contacts 39 are closed, thus providing the desired alternating actuation for the two tappers 9.

A first variable resistance 42 is incorporated in the circuit, and this is adjusted during manufacture to provide rough calibration of the circuit output and, therefore, of the amplitude of, the pulse or tap. In the preferred embodiment, there is a second variable resistor 43 which can be adjusted by the user to vary the amplitude of the tap in response to sifting conditions.

The operating circuit components, other than the coils 21, are preferably housed in a separate control box (not shown) on or near the sifter.

The preferred embodiment shown and described provides a highly efiicient tapper which is relatively simple and inexpensive. It should be apparent, however, that modifications in arrangement, structure, and use are possible without departure from the spirit of the invention. The invention is, therefore, not intended to be limited by the showing herein or in any other manner except as may specifically be required.

I claim:

1. In a sifter having a sieve stack assembly-including at least one sieve having a horizontally oriented screen and a rigid outer ring that surrounds and supports the periphery of the screen and that defines a vertical cylindrical inner surface,

the combination with said sieve of a tapper assembly comprising: a rigid mounting ring aligned with and vertically adjacent to the sieve ring that defines a vertical cylindrical inner surface substantially continuous with the inner surface of the sieve ring; a tapper mounted on the outside of the mounting ring that includes a pin that is vertically spaced from the mounting ring to lie in a horizontal plane at the level of the sieve ring, the pin being oriented radially with respect to the sieve ring to present an end that faces and is engageable with the sieve ring, the pin being movable along its own axis toward and away form the sieve ring; and actuating means to periodically move the pin against the sieve ring to deliver a mechanical tap thereto.

2. The tapper assembly of claim 1 wherein the actuating means comprises an electrical coil disposed around the pin, and the pin has an inner end facing and engageable with the sieve ring and an outer end which projects away from the sieve and beyond the coil, and there is a magnetic tapper bar facing the outer end of the pin which is attracted toward the coil when the coil is energized and which then engages the outer end of the tapper pin to move the pin against the sieve ring.

3. The tapper of claim 2 wherein there is an L-shaped stationary magnetic arm which has a first leg extending across the end of the coil corresponding to the inner end of the pin and a second leg parallel to the coil axis; and the tapper bar is L-shaped and includes a base leg which faces and overlaps the second leg of the arm and a tapper leg adapted to engage the outer end of the pin; 

1. In a sifter having a sieve stack assembly including at least one sieve having a horizontally oriented screen and a rigid outer ring that surrounds and supports the periphery of the screen and that defines a vertical cylindrical inner surface, the combination with said sieve of a tapper assembly comprising: a rigid mounting ring aligned with and vertically adjacent to the sieve ring that defines a vertical cylindrical inner surface substantially continuous with the inner surface of the sieve ring; a tapper mounted on the outside of the mounting ring that includes a pin that is vertically spaced from the mounting ring to lie in a horizontal plane at the level of the sieve ring, the pin being oriented radially with respect to the sieve ring to present an end that faces and is engageable with the sieve ring, the pin being movable along its own axis toward and away form the sieve ring; and actuating means to periodically move the pin against the sieve ring to deliver a mechanical tap thereto.
 2. The tapper assembly of claim 1 wherein the actuating means comprises an electrical coil disposed around the pin, and the pin has an inner end facing and engageable with the sieve ring and an outer end which projects away from the sieve and beyond the coil, and there is a magnetic tapper bar facing the outer end of the pin which is attracted toward the coil when the coil is energized and which then engages the outer end of the tapper pin to move the pin against the sieve ring.
 3. The tapper of claim 2 wherein there is an L-shaped stationary magnetic arm which has a first leg extending across the end of the coil corresponding to the inner end of the pin and a second leg parallel to the coil axis; and the tapper bar is L-shaped and includes a base leg which faces and overlaps the second leg of the arm and a tapper leg adapted to engage the outer end of the pin; and there is a spring connecting the said base and second legs which allows the tapper arm to pivot toward the pin upon energization of the coil and which returns the tapper arm to a retracted position removed from the pin upon de-energization of the coil.
 4. The tapper of claim 3 wherein there is a spring bias means which operates to hold the inner end of the tapper pin against the sieve ring at all times. 